Electrolux PQ91-40GG 21.6V Replacement Battery 2000mAh

Electrolux PQ91-40GG Series — 21.6V Li-ion Replacement Battery (405 54 78-29/3)

This is a 21.6V, 2000mAh (43.2Wh) Li-ion battery for the Electrolux PQ91-40GG and related cordless stick vacuum models. It replaces OEM part numbers 405 54 78-29/3, 4055478293, and 140231463013. Compatible models include PQ91-40GG, PQ91-P40GG, ES62AB25UG, and ES62CB25DH, among others.

• PQ91 and ES62 series compatibility: These models share the same 21.6V battery platform, connector pinout, and BMS handshake protocol. Swapping between them requires no modification — the cell pack seats and communicates identically across the series.
• Bench tested on actual hardware: We cycled this battery through load and discharge on a PQ91-series unit. The BMS held voltage within spec under sustained motor draw and triggered no false overcurrent trips during normal operation.
• Dock charging habit on cordless vacuums: Do not leave this vacuum sitting on the charging dock indefinitely. Continuous trickle charge accelerates capacity fade on Li-ion cells in this voltage class. Charge to full, then remove from the dock.

Suction dropping before the battery indicator reaches low

The PQ91 motor draws harder when airflow is restricted — a partially blocked filter forces higher current at the same fan speed. The BMS reads this as increased load and throttles output voltage to protect the cells, which the user experiences as suction loss rather than a battery warning. The indicator is tied to state-of-charge, not motor load, so it stays green while performance falls. Clean or replace the filter before replacing the battery — this resolves the symptom in most cases.

Motor cutting out mid-clean and then recovering after a few seconds

This is a BMS overcurrent trip, not a power switch fault. When the vacuum draws above the BMS current threshold — usually caused by a blockage at the brush head or a clogged post-motor filter — the protection circuit opens and shuts the motor down. The BMS resets automatically after a short cooldown, which is why the vacuum restarts on its own. Clear any blockage, check both filters, and confirm the battery rests at or above 21.6V on a multimeter before ruling out cell degradation.